Room‐Temperature Out‐of‐Plane Ferroelectricity and Resistance Switching Based on 2D Bi2O2Se

Abstract Although 2D Bi2O2Se plays an important role in the electronics and optoelectronics based on its in‐plane property, its out‐of‐plane electrical transport behavior remains unclear, especially in fabricating vertical devices with high integration density for novel functionality. Here, a solution‐processed method is developed to prepare 2D Bi2O2Se with mass production (e.g., hundreds of milliliter scale). The out‐of‐plane ferroelectric property of 2D Bi2O2Se is observed by piezoresponse force microscopy and the ferroelectric dipole map atom‐by‐atom at the Bi2O2Se surface, which shows an atomically resolved dipolar displacement of Se ions. The out‐of‐plane resistant switching property of 2D Bi2O2Se is revealed by conductive atomic force microscopy. Moreover, the electric field on the local polarization of Bi2O2Se is addressed by using ab initio simulations, which shows a broken inversion symmetry along the z‐axis of Bi2O2Se. The working mechanism of resistant switching behavior in Bi2O2Se is attributed to the diffusion and shuttle of Se ions. Besides, a controllable wet‐assembled method is developed to prepare Bi2O2Se thin film with centimeter scale and explores its application on photodetectors under 808 nm laser light. This work reveals the unique out‐of‐plane transport behavior of 2D Bi2O2Se, providing the basis for fabricating multifunctional devices with high integration based on this 2D material.